Transgenic construct that contains the Ecol\lacZ^Hsp70Bb.-190 reporter, which is sensitive to silencing by heterochromatin, and a w^+* minigene that includes the eye-specific enhancer element. The reporter and w^+* minigene are flanked by an scs element and a scs' element, to insulate them from euchromatic position effects; this is designed to ensure that any lacZ expression accurately reflects the extent of heterochromatic silencing.

Hsp70 promoter, 5' untranslated region (UTR) and first seven codons are fused to the lacZ coding region, Hsp70 3' UTR sequences are present.